Integral membrane proteins (IMPs) are essential for cell function and comprise more than 50% of human drug targets. However, they are difficult to solubilize and purify from cell membranes while maintaining their natively folded structures and functions. IMPs are notoriously difficult to handle because of their instability and their tendency to lose function outside the lipid bilayer. Detergents, structurally similar to cellular lipids with an alkyl chain at one end and a polar head group at the other, are indispensable for the solubilization and purification of IMPs. However, IMPs tend to denature or aggregate in the presence of common detergents, which presents a significant challenge for manipulating the proteins during biochemical assays and structural analysis. The development of new types of amphiphilic molecules that can stabilize IMPs would therefore be of great value for both functional and structural investigation.
Also, only a small number of high resolution crystallographic structures of IMPs are available to date because of the difficulties of their isolation, purification, and crystallization. Numerous detergents are screened when investigators seek to isolate and purify new membrane proteins. The screening remains an expensive and labor-intensive task with a low rate of success. Thus, new detergents for IMPs are needed in the art.
Cholic acid and deoxycholic acid are naturally occurring bile acids that display a degree of facial amphiphilicity due to the orientation of multiple hydroxyl groups on one face of the rigid hydrophobic steroid skeleton. They and their derivatives have broad application in various fields, including in membrane chemistry and biochemistry, as detergents, as well as in molecular recognition studies. Previous attempts to use this motif in membrane biochemistry featured the replacement of carboxylic acid group at one end of cholic acid with other polar head groups to provide, for example, CHAPS (3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate) and CHAPSO (3-[(3-cholamidopropyl)-dimethylammonio]-2-hydroxy-1-propanesulfonate), which are now widely commercially available. Yet these compounds do not sufficiently alleviate the problems associated with solubilizing and purifying membrane proteins, and other needs in the fields of membrane chemistry and biochemistry. Accordingly, new detergent molecules are clearly needed to aid membrane research endeavors.